Enzymes


Uploaded by bozemanbiology on 26.11.2011

Transcript:



Hi. It's Mr. Andersen and welcome to Biology Essentials video 48. This podcast
is on enzymes. Enzymes remember are chemicals that aren't consumed in a reaction but can
speed up a reaction. One of the major ones we'll talk about this year in AP bio is called
catalase. Catalase is an enzyme that's found in almost all living cells, especially eukaryotic
cells. But what it does is it breaks down hydrogen peroxide. Hydrogen peroxide you probably
knew growing up, you'd put it on a cut maybe and it would bubble or you could use it to
bleach your hair. That's pretty dilute hydrogen peroxide. Actually concentrated hydrogen peroxide,
this is somebody who's touch 30% hydrogen peroxide, it damages and kills cells. And
so hydrogen peroxide is just produced naturally in chemical reactions but your cell has to
get rid of it before it builds up an appreciable amounts. And it uses catalase to do that.
And so if we were to look at the equation, so we've got hydrogen peroxide or H2O2 is
going to breakdown into two things. One is water and the other one is O2, oxygen. And
so this is not a balanced reaction. So if I put a 2 there and I put a 2 here, so hydrogens
I've got 4, 4. Oxygens I've got 4, so perfect. So this is a balanced equation. So you've
got 2 hydrogen peroxide breaking down into 2 water molecules and 1 oxygen molecule. But
it does that using an enzyme. And so in other words, hydrogen peroxide, let me get my arrows
to fit in here is going to feed into catalase and it's going to break that down into these
2 products, water and oxygen. And it does that at an incredible rate. I was reading
that 40 million hydrogen peroxides will go into a catalase and be broken down into water
and oxygen, 40 million every second. And so it's incredibly fast at breaking down that
hydrogen peroxide into something that it can use. And so how does it do that? Well that's
what I'm going to talk about. And so basically an enzyme, let me try and draw an enzyme,
so if an enzyme looks like this. It's a giant protein, so if we say it looks like that,
it's going to have an area inside it called the active site. And so the active site, let's
see how I could do this, good, so the active site is basically going to be a part on the
enzyme where there's a hole in it. So this is this giant protein, it's got an active
site, and the substrate is going to fit into to it. And so going back to how do enzymes
work, well the active site is going to be an area within the enzyme, so this would be
the enzyme here, and basically the substrate fits into it. And so what was the example
we were just talking about? The enzyme was catalase. What was the substrate? Substrate
is H2O2 or hydrogen peroxide. So that's how enzymes work. It basically tugs on the substrate
and breaks it down. It's very important in chemical reactions. And sometimes we want
to turn on enzymes and sometimes we want to turn off enzymes. And so in every step of
photosynthesis, in every step of cellular respiration, glycolysis, citric acid cycle,
all of those chemical reactions remember have to have an enzyme that's associated with them
that can speed up that reaction. And so it's really important that we sometimes activate
or turn on those enzymes. It's also just as important that sometimes we turn them off.
And so there are two types of inhibition. Inhibition can either be competitive, that's
where a chemical is blocking the active site or allosteric when we're actually changing
the shape or giving it another shape. Chemical reactions, another important thing that we
want to measure with them is the rate of a chemical reaction. We can do that by either
measuring the reactants or the products. So let me stop talking about what I'm going to
talk about and actually talk about it. And so here is our enzyme. Our enzyme that we
talked about is called catalase. So catalase is going to be a protein. It has a specific
shape and so if we go down here to the enzyme, this would be the enzyme right here, it's
going to have an active site. An active site is the area when the substrate can fit in.
And so the substrate is going to be this green thing in this picture. It'll fit right in
here. It fits almost like a key fits a lock. And so it's going to be a perfect fit between
the two. Every chemical reaction is going to have a different enzyme that breaks that.
And so the important part is right here. So now once we have the enzyme inside the active
site, there's going to be a chemical tug. In other words it's going to pull on that
chemical. It's going to lower it's activation energy so it can actually break apart into
its products. And so if this is our H2O2 right here, there's going to be a tug on those chemicals.
Sometimes it will actually change the pH, sometimes it'll put a mechanical tug on it,
but basically what it's going to do is it's going to make it easier for those chemicals
to spontaneously break apart. Now hydrogen peroxide by itself, H2O2, if you leave it
in a bottle for millions and millions of years, if you come back it's spontaneously going
to break down into water and oxygen but that's going to take years and years and years to
do that. And with an enzyme it can happen in seconds. It's like I said, 40 million hydrogen
peroxides can feed through this, create all of this water and can do that really really
quickly. And so enzymes are ready to go and so we want to control which enzymes are firing
at which time and which ones are being released. And so there's basically a turn on and then
there's a turn off. And so how do we turn enzymes on? Well there's two ways that we
can do that. Number 1, we could just not produce them until they're needed. And so lots of
times we won't produce a protein until it's required and so we do what's called gene regulation,
where we don't even code those proteins until we're ready to use them. But also we can activate
them. And so activation is adding something to an enzyme to actually make it work. And
so you don't have to remember the names of these, but this is succinate dehydrogenase
and it's a cool enzyme that's used both in the citric acid cycle and the electron transport
chain. So this is going to be on, it's going to be embedded in that inner mitochondrial
membrane and so it's going to run two specific reactions. So it's going to convert certain
reactants into products. But if you just build succinate dehydrogenase by itself, it doesn't
do anything. It's not going to work. It has to be activated. And so there are two type
of activators. Those that are called cofactors and those that are called coenzymes. And so
if you were to look in here there's going to be things that have to be added to that
enzyme before it can actually function. And so the two types are cofactors, coenzymes.
I came up with some that you might know. Cofactors are basically going to be small chemicals
that are inorganic. What that means is they're not made up of carbon. And so heme is an example
of a co-factor. Heme is also what's found in blood. It has an iron atom in the middle
and so that's why we call it hemoglobin. And so what it does is it's creating that hemoglobin
protein and activating it. And so cofactors are going to be inorganic. And so in other
words they are not containing carbon. And then we're going to have coenzymes and those
are going to be organic. And so they're helping that enzyme to work. An example of a coenzyme
would be thiamine. And so thiamine, another name for that is vitamin B1. And so vitamins
are a required organics that we need inside our diet and they help enzymes function. And
if you don't get enough vitamin B1 in your body then you die as a result of the neurological
issue. And same thing with cofactors. So these are required for life. But basically what
happens is once we have the cofactors and the coenzymes now we have an enzyme that can
actually function. And now it can do what it's meant to do. But if we remove those cofactors,
if we remove those inorganics and those organics then it will actually come to a stop or it
won't function anymore. So that's activation. That's how we turn enzymes on. But sometimes
we want to turn them off. And so let me kind of get you situated. We've got our enzyme
here, we've got our substrate that's going to fit here so if you think about it as an
engineer for a second, how could we stop that substrate, again 40 million of them coming
through the active site in catalase? How do we slow it down? Well there are two types
of inhibition. First on is called competitive inhibition. Competitive inhibition is when
you use an inhibitor, which is another chemical and you just get that to bond into the active
site. So if you have that bonding in the active site then that substrate can't fit in and
so we're going to stop the reaction. So if we make an inhibitor that bonds to the active
site we call that competitive inhibition because it's competing for the space with the substrate.
Now we can also do that non-competitive inhibition and we usually call that allosteric. Allosteric
reaction works the same way. Here we are. We've got our enzyme. Here's our substrate.
It's trying to fit into the active site. We also have what's called an allosteric site,
which is going to be another site on the enzyme itself. And so one type of allosteric or changing
the shape inhibition that we can do is we can have an inhibitor now that's just going
to bond to that allosteric site. When it bonds to the allosteric site it's covering up the
active site and so now there's going to be no way that that substrate can fit in. But
since it's not actually bonding to the active site we call that allosteric. Allosteric means
different shape or different shape of the enzyme. So that's a type of non-competitive
inhibition. Or we can do it this way. So this would be another type of allosteric inhibition.
We can have an inhibitor bond to an allosteric site, but if you look at the active site in
this picture, here's the active site, once this inhibitor bonds with the allosteric site
it now changes the shape of the active site. Once you've changed the shape of the active
site, remember the substrate only fits if it's like a lock and a key, now it's not going
to fit anymore. And so this is another type of allosteric inhibition. And so we use feedback
loops and we use inhibitors and cofactors and coenzymes to regulate what enzymes are
going off at what time. Now when we do the enzyme lab we are using catalase. And so when
we do it in class we're using catalase. It's an enzyme we use, an enzyme that's found in
yeast. We then fill up a beaker with hydrogen peroxide. We put our little disks of filter
paper or chads at the bottom. We dip them in varying concentrations of the enzyme and
we then see how long it takes for them to float up. And so what we're varying or the
independent variable is going to be, the independent variable is going to be the amount of the
enzyme. And the dependent variable is going to be how long it takes for them to float
or the number of floats per second. And so you can imagine, let me get a better color,
if I increase the concentration of the enzyme, we're going to increase the rate of the reaction.
But eventually you can see how it starts to level off here. Eventually if you have enough
of those, let me change to a different color, eventually it's going to level off. And so
when we're measuring reaction rate we could measure two things. We could measure the products
that are created or we could measure the amount of reactants that are being consumed. In the
enzyme lab we're measuring the amount of oxygen so we're measuring the amount of products
that are created. But there's other things we could measure in this. Not only the concentration
of the enzyme, we could measure the temperature, we could measure the pH. We could measure
a lot of different things and remember organisms, if we were to measure temperature for example
the reaction rate's going to increase and eventually the enzyme is going to denature
and so there's going to be an optimum set point. And since you have an internal temperature
of 37 degrees celsius, most of the enzymes inside your body are prime to work at that
specific rate. And so that's enzymes and they are used to maintain that internal balance
and I hope that's helpful.